$\begin{cases} f(1)=72 \\\\ f(n)=f(n-1)+9 \end{cases}$ Find an explicit formula for $f(n)$. $f(n)=$
Explanation: From the recursive formula, we can tell that the first term of the sequence is ${72}$ and the common difference is ${9}$. This is the explicit formula of the sequence: $f(n)={72} +{9}(n-1)$ Note that this solution strategy results in this formula, however an equally correct solution can be written in other equivalent forms as well.